PHOENIX — Hundreds of children who crossed the U.S. border illegally were transported to Arizona from Texas over the weekend as border agents face a surge of unauthorized Central American migrants entering the country, authorities said on Monday.

Nearly 1,000 unaccompanied minors have been sent in the last week from overflowing facilities in southern Texas to a large, former warehouse building in Nogales, Arizona, border patrol officials said.

The Obama administration said on Monday it was designating a third U.S. military base – in Fort Sill, Oklahoma – as emergency housing for hundreds of children immigrating illegally to the United States without parents or relatives.

 The immigrant children from the Rio Grande Valley in Texas are flown to Tucson and then bused to Nogales for processing at a makeshift spot that serves meals and is fitted with beds, showers and bathrooms.

Adame said the goal is for the youngsters to spend no more than 72 hours at the Tucson building before being transported to emergency shelters in San Antonio, Texas, Ventura County in Southern California, and Fort Sill in Oklahoma.

Arizona Governor Jan Brewer, a Republican, has clashed repeatedly with President Barack Obama’s administration over illegal immigration. She complained a week ago after learning families were being shipped to Arizona from Texas for processing and then released at bus stations.

Federal officials under Obama have focused on turning back unauthorized immigrants stopped in border regions and deporting others outside of those areas who are convicted of crimes.

 Brewer and other republicans say the Obama administration has failed to secure the U.S. southern border. Meanwhile, a number of other groups are pushing for policy reform to allow the estimated 11 million undocumented immigrants in the country to obtain a pathway to U.S. citizenship.